April 30, 2012

Cochlear Implants Made Small Enough To Fit Inside The Ear

Researchers are developing a tiny middle ear "microphone" that could remove the need for any external components on cochlear implants. Led by University of Utah engineer Darrin J. Young, the research team has produced and tested a prototype of the device which uses an accelerometer attached to the tiny bones of the middle ear to detect sound vibration.

Cochlear implants have restored basic hearing to some 220,000 deaf people, yet a microphone and related electronics must be worn outside the head, raising reliability issues, preventing patients from swimming and creating social stigma.

Now, a University of Utah engineer and colleagues in Ohio have developed a tiny prototype microphone that can be implanted in the middle ear to avoid such problems.

The proof-of-concept device has been successfully tested in the ear canals of four cadavers, the researchers report in a study just published online in the Institute of Electrical and Electronics Engineers journal Transactions on Biomedical Engineering.

The prototype – about the size of an eraser on a pencil – must be reduced in size and improved in its ability to detect quieter, low-pitched sounds, so tests in people are about three years away, says the study’s senior author, Darrin J. Young, an associate professor of electrical and computer engineering at the University of Utah and USTAR, the Utah Science Technology and Research initiative.

The study showed incoming sound is transmitted most efficiently to the microphone if surgeons first remove the incus or anvil – one of three, small, middle-ear bones. U.S. Food and Drug Administration approval would be needed for an implant requiring such surgery.

The current prototype of the packaged, middle-ear microphone measures 2.5-by-6.2 millimeters (roughly one-tenth by one-quarter inch) and weighs 25 milligrams, or less than a thousandth of an ounce. Young wants to reduce the package to 2-by-2 millimeters.

In conventional cochlear implant, there are three main parts that are worn externally on the head behind the ear: a microphone to pick up sound, a speech processor and a radio transmitter coil. Implanted under the skin behind the ear are a receiver and stimulator to convert the sound signals into electric impulses, which then go through a cable to between four and 16 electrodes that wind through the cochlea of the inner ear and stimulate auditory nerves so the patient can hear.

“It’s a disadvantage having all these things attached to the outside” of the head, Young says. “Imagine a child wearing a microphone behind the ear. It causes problems for a lot of activities. Swimming is the main issue. And it’s not convenient to wear these things if they have to wear a helmet.”

Young says the microphone also might be part of an implanted hearing aid that could replace conventional hearing aids for a certain class of patients who have degraded hearing bones unable to adequately convey sounds from conventional hearing aids.

To hear a regular recording of the start of Beethoven’s Ninth Symphony, click here.

To hear the start of Beethoven’s Ninth Symphony, recorded through a new microphone in the middle ear of a cadaver, click here.